如何检查是否System.Net.WebClient.DownloadData正在下载的二进制文件？

问题描述

我想使用 Web客户端来下载使用WinForms应用程序从网页文件。不过，我真的只是想下载HTML文件。任何其他类型的，我会想要忽略。

I am trying to use WebClient to download a file from web using a WinForms application. However, I really only want to download HTML file. Any other type I will want to ignore.

我查了 WebResponse.ContentType ，但其价值始终是空。

I checked the WebResponse.ContentType, but its value is always null.

任何人有任何想法可能是什么原因呢？

Anyone have any idea what could be the cause?

推荐答案

鉴于你的更新，您可以通过GetWebRequest改变。方法做到这一点：

Given your update, you can do this by changing the .Method in GetWebRequest:

using System;
using System.Net;
static class Program
{
    static void Main()
    {
        using (MyClient client = new MyClient())
        {
            client.HeadOnly = true;
            string uri = "http://www.google.com";
            byte[] body = client.DownloadData(uri); // note should be 0-length
            string type = client.ResponseHeaders["content-type"];
            client.HeadOnly = false;
            // check 'tis not binary... we'll use text/, but could
            // check for text/html
            if (type.StartsWith(@"text/"))
            {
                string text = client.DownloadString(uri);
                Console.WriteLine(text);
            }
        }
    }

}

class MyClient : WebClient
{
    public bool HeadOnly { get; set; }
    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest req = base.GetWebRequest(address);
        if (HeadOnly && req.Method == "GET")
        {
            req.Method = "HEAD";
        }
        return req;
    }
}

另外，你可以重写GetWebRespons（）的时候，也许是抛出一个异常，如果它是不是你想要的检查头：

Alternatively, you can check the header when overriding GetWebRespons(), perhaps throwing an exception if it isn't what you wanted:

protected override WebResponse GetWebResponse(WebRequest request)
{
    WebResponse resp = base.GetWebResponse(request);
    string type = resp.Headers["content-type"];
    // do something with type
    return resp;
}

这篇关于如何检查是否System.Net.WebClient.DownloadData正在下载的二进制文件？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！